The world champion, who has a 17-point lead over Vettel after five races, made a few errors that compromised his overall lap time.

But there will be questions as to whether Mercedes are struggling in Monaco for the second year in succession after he said over the radio that something did not feel right while he was doing a race-simulation run on the super-soft tyre, the hardest of the three compounds available this weekend.

Running in race trim on the hyper-soft, Vettel appeared to have a pace advantage over Hamilton of about 0.3secs, although practice times are not always an accurate measure of actual form.

Renault’s Nico Hulkenberg was seventh fastest, ahead of the McLarens of Stoffel Vandoorne and Fernando Alonso, the latter’s day compromised slightly by losing most of the first session because of a brake-by-wire issue.

Haas, who impressed at the last race in Spain with Kevin Magnussen finishing sixth, well clear of the other midfield runners, appeared to be struggling, the Dane 16th with team-mate Romain Grosjean two places further back.

There was only 0.5secs between Hulkenberg in seventh and Sauber’s Charles Leclerc in 17th.

Behind the scenes, Ferrari are the subject of an investigation into the operation of the energy store in their hybrid system by governing body the FIA, who are concerned that it could be used in an unscrupulous way.

Despite its concerns, the FIA has no evidence it has been used in such a manner and insiders say the FIA, after an inquiry lasting more than a month, is moving towards a position where it is satisfied there is no chance the energy store can be used in a way it should not be.